Description of the Related Art
The present invention relates to an individual device for measuring the neutron dose equivalent and which is more particularly applicable to radiation protection.
The safety of technical and research personnel who may be exposed to radiation means that it is constantly necessary to monitor the doses absorbed in the form of a dose equivalent corresponding to the biological risk of the physical measurement. It is in particular important to determine the neutron flux and by conversion, as a result of conversion coefficients experimentally and theoretically defined by the International Commission on Radiation Units (ICRU), the neutron dose equivalent.
Several devices are known making it possible to determine the neutron dose equivalent.
A first device uses the neutron albedo on a body, which produces a low energy neutron flux irradiating a thermoluminescent material. On heating the irradiated body, the latter emits light in proportion to the dose received. This device suffers from the disadvantage of being a passive system, which only supplies the result of the measurement after heating, so that it is not possible to follow in real time the evolution of the absorbed doses.
Another type of passive detector is the solid state detector. A film subject to irradiation records traces corresponding to each passage of a charged heavy particle. The film is supported by a badge worn by the user.
In order to give a reading the film is developed and this operation generally takes about 4 hours. Then each recorded trace is associated with the passage of a particular particle type and then the neutron flux density is determined, which makes it possible to calculate the dose equivalent. Here again, the measurement is not instaneous. The reading of the traces is an arduous task requiring a considerable amount of time, roughly a week being needed to process about 100 badges.
Another type of device called the "tissue equivalent proportional counter" is formed by a cathode produced from a material equivalent to a biological tissue which, under the effect of a neutron bombardment, emits charged secondary particles. The measurement of the energy loss of these particles during the passage of a gas equivalent to a biological tissue makes it possible to determine the dose equivalent. In order to be able to operate such a device requires a power supply able to provide a voltage between 500 and 1000 V, which leads to the obvious problems and dangers for the user as a result of the use of a high voltage.